Machines have heretofore been developed and utilized for wrapping battery plates in a web of material and then sealing the two opposed overlapping edges of the material to form an enclosing pouch open at the top end of the battery plate. See for example the disclosures of U.S. Pat. No. 3,900,341 to Schoichiro and the disclosure of application Ser. No. 475,480 filed June 6, 1974 by the instant inventor and John P. Badger, now U.S. Pat. No. 4,063,978.
These machines achieved a folding of the web around the battery plate by suspending a length of the web in front of a slot and then passing the battery plate horizontally through said slot to effect the wrapping of the web around the battery plate. As the wrapped plate emerged from the slot, however, prior art machines employed either continuously moving belts or rollers to engage the wrapped plate and pull it the remainder of the way through the slot and also hold the web material in position during the edge sealing operation. This type of mechanism for advancing the wrapped plate through the sealing operation proved to be inefficient for several reasons. In the first place, as is well known in the art, a battery plate is a relatively non-uniform article and may not have its bottom edge normal to its lateral sides. Further, a plate is normally provided with a plurality of integral ribs. Advance of the plate bottom against the web may misalign the plate with respect to its enfolding sheet. In addition it is difficult for belt or roller type conveying mechanisms to achieve a firm, non-slipping engagement of the web relative to the enclosed battery plate. Where heat seals are applied to thermoplastic enveloping material advanced as a plate envelope, the application of heat to the thermoplastic material may result in some distortion of the material due to the fact that any thermoplastic plastic material produced in sheet form normally has some degree of orientation incorporated in the material as an inherent result of the sheet forming process. The application of heat to effect the sealing operation results in a tendency of the plastic material to shrink and crinkle and this distorts the position of the plastic material relative to the battery plate or, even worse, effects a displacement between the normally overlapping edges of the plastic material which are to be heat sealed together. As a result, the pouches produced by the prior art machines have not been characterized by a high degree of uniformity and, in some instances, defective pouches have resulted due to the fact that the material is sufficiently displaced or skewed relative to the enclosed battery plate so that it is impossible to achieve contact between and a bond along the entire length of the overlapped edges of the material.
Another deficiency of prior art machines, where the sheet material was fed as a continuous web, lies in the fact that the web was not maintained under strict control during the entire period that it was being inserted into the slot and wrapped around the battery plate. For example, the web in the abovementioned prior patent application was severed before the battery plate had progressed any substantial distance into the web folding aperture slot and in effect, the battery plate caught the plastic material on the fly and forced it into the folding slot. This often resulted in inaccuracies in the length of the folded material relative to the enclosed battery plate. One side of the pouch would be higher or lower than the other side.
Accordingly, it is an object of this invention to improve machines for enclosing battery plates within a pouch formed from a sheet of material.
Another object is to maintain registry of a battery plate with a sheet during the formation of the sheet into an enclosing pouch.
A further object is to accurately establish lengths of sheet derived from a continuous web and to position the sheet lengths for precise folding into battery plate receiving pouches.
A fourth object of this invention is to provide an improved plate wrapping machine wherein the web of thermoplastic material to be wrapped around the battery plate is maintained under control at all points in the cycle of operation so that the web is accurately positioned relative to the battery plate and maintained in such accurate relationship as the wrapping operation progresses.
A particular object of this invention is to maintain a plate centered in the web of sheet material in which it is to be enveloped to cause the web of material to wrap around the battery plate by gripping the wrapped edge of the plate and effectively locking the wrapping material in position against the enclosed battery plate as the remainder of the operation proceeds and particularly while the overlapping edges of the web material are sealed together.
Other objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the annexed sheets of drawings.